Je suis en quelle année?

Describing what school you attend is a simple translation.

I am in middle school.	Je suis un(e) collégien(ne).
You are in high school.	Tu es un(e) lycéen(ne).
She is in college.	Elle est une étudiante à l'université.

Translating grade levels in French, however, can be more complicated. Learn how from this chart (adapted from FrenchEntrée.com).

...Age...	...Année scolaire en France...	...Ecole français...	...US grade level or year...	...US school...
3	maternelle petite	école maternelle		nursery
4	maternelle moyenne			pre-K
5	maternelle grande			kindergarten
6	cours préparatoire	école primaire	1st	elementary
7	cours élémentaire niveau 1		2nd
8	cours élémentaire niveau 2		3rd
9	cours moyenne niveau 1		4th
10	cours moyenne niveau 2		5th	elementary, junior high, or middle
11	6ème		6th	elementary, junior high, or middle
12	5ème	collège	7th	junior high or middle
13	4ème		8th	junior high or middle
14	3ème	lycée	9th or freshman	high school
15	2ème		10th or sophomore
16	1ère		11th or junior
17	terminale		12th or senior

Alors, un élève de "8th grade" dit: Je suis en 4ème année.
So, an 8th grade student says: I am in 4th year.

Looking for a more visual representation? Look at this PDF developed by EuropUSA.